In situ TEM study of the sodiation/desodiation mechanism of MnO₂nanowire with gel-electrolytes

In this work, in situ transmission electron microscopy study of the electrochemical sodiation and desodiation processes was performed in a nanobattery which consisted of a single MnO2nanowire and different kinds of gel-electrolyte. It is found that after full sodiation, single crystalline MnO2nanowire is transformed to a mixed nanocrystalline phases of Na2O and MnO, and the following cycles are controlled by the reversible conversion reaction between NaMnO2and MnO. Both in situ electrochemical test and ex situ battery test show that the glyme-based gel-electrolyte is more suitable for the MnO2nanowires anode materials. It is also revealed that the MnO2nanowire expansion ratio strongly depends on the diameter of the nanowires. This work provides a new insight on the sodiation/desodiation mechanism in MnO2nanowire and gel-electrolyte, and may pave the path for the development of practical sodium-ion batteries with gel-electrolyte.